The invention concerns a circuit for detecting an overload in a load supplied by a switched-mode power supply, comprising: a first comparator of a first voltage based on the supply voltage of the load relative to a first threshold, supplying a regulating signal to a pulse generator controlling the switched-mode power supply; a second comparator of a second voltage relative to a second threshold, supplying a signal indicating the presence of an overload; and means for automatically controlling said second voltage by a third threshold lower than the second and higher than the first, and for deactivating the second comparator as long as said automatic control is maintained.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A circuit for detecting an overload in a load supplied by a switch-mode power supply, comprising: a first comparator of a first voltage with respect to a first threshold, the first voltage being a function of a load supply voltage, the first comparator providing a regulation signal to a generator of control pulses of the switch-mode power supply; a second comparator of a second voltage with respect to a second threshold, the second comparator providing a signal at its output indicative of the presence of an overload, the second voltage being different from the first voltage after starting of the circuit is completed; and a subcircuit that controls the value of said second voltage, the subcircuit receiving a third threshold smaller than the second threshold and greater than the first threshold, the output of the second comparator being low as long as the second voltage is less than or equal to the third threshold.
2. The circuit of claim 1 wherein said subcircuit comprises a third comparator of said second voltage with respect to the third threshold, the third comparator configured to provide a control signal to an element operable to short-circuit a constant current source of charge, the circuit of claim 1 further comprising a capacitor connected to ground, across which said second voltage is measured.
3. The circuit of claim 2 , further comprising a means for precharging said capacitor to said third threshold on a power-on of the circuit.
4. The circuit of claim 1 wherein said second and first voltages are sampled between the terminals of a dipole behaving as a current source, the value of which is a function of the voltage across the load.
5. The circuit of claim 4 wherein said dipole is a bipolar transistor.
6. The circuit of claim 5 wherein said transistor is an NPN-type transistor having its emitter connected to ground by an at least resistive passive circuit.
7. The circuit of claim 6 wherein the value of the passive circuit is selected to deliver a current when the transistor is in the on state, which is smaller than the constant current provided by the current source.
8. The circuit of claim 6 , further comprising a means for forcing the first voltage to said third threshold on a power-on of the circuit, said at least resistive passive circuit being a resistive and capacitive circuit.
9. The circuit of claim 6 wherein the transistor is a phototransistor of an optocoupler.
10. The circuit of claim 1 wherein the second comparator controls an element for providing a control current to a pulse generation circuit.
11. A circuit for detecting an overload in a load comprising: a first logic circuit that receives a first voltage at a first input which represents a load supply voltage, receives a first threshold voltage at a second input, and outputs a regulation signal based on the inputs; a comparator that receives a second voltage at a first input and receives a second threshold voltage at a second input, the comparator providing a signal at its output indicative of the presence of an overload, the first and second voltages being different from each other after starting of the circuit is completed; and a second logic circuit that varies the value of said second voltage by switchably bypassing a constant current source, the second logic circuit being switchable to receive at a first input either the first voltage or the second voltage in addition to a third threshold voltage, the second logic circuit being configured to receive said second voltage at a second input and output a control signal based on the inputs, the output control signal coupled to vary the value of the second voltage.
12. The circuit of claim 11 wherein said second logic circuit comprises a third comparator of said second voltage with respect to the third threshold voltage and provides the control signal to an element operable to short-circuit the constant current source, the constant current source configured to charge a capacitor connected between the second voltage and ground and across which capacitor said second voltage is measured.
13. The circuit of claim 11 wherein the first logic circuit is a comparator.
14. The circuit of claim 11 wherein the first logic circuit includes an operational amplifier.
15. The circuit of claim 1 wherein the first comparator is an operational amplifier configured as a linear comparator.
16. The circuit of claim 1 wherein the second comparator is an operational amplifier configured as a linear comparator.
17. The circuit of claim 1 wherein the subcircuit includes a third comparator that is an operational amplifier configured as a linear comparator.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
February 6, 2007
November 2, 2010
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